Method of making water laid,stained wood sheet



Nqv. 24', 1970 M. J/SHOWAL'I'ER T L METHOD OF MAKING WATER LAID, STAINEDWOOD SHEET med Dec 1; 1967 means 'INVENTORS MERLE J- SHOWALTER mcrmao J-nonznwmraa PRODUCT .M Mr R S; D A m W L G Y R J l MR U B m m m 5 W N anY1. .l m m a S 5 MM D w .W m R N E I T T m as Ew 1 m GRAIN PATTERN.EMPHASIZED BY DIFFERENT COLORING,

sues? :OF WATER-LAID wooo FIBERS ATTORNEY United States Patent O3,542,641 METHOD OF MAKING WATER LAID, STAINED WOOD SHEET Merle J.Showalter and Richard J. Hohenwarter, Lancaster, Pa., assignors toArmstrong Cork C0., Lancaster, Pa., a corporation of Pennsylvania FiledDec. 1, 1967, Ser. No. 687,282 Int. Cl. D21f 11/00 U.S. Cl. 162-134 3Claims ABSTRACT OF THE DISCLOSURE Method, and product, of making apatterned wood sheet by forming a sheet of wood fibers from an aqueousslurry and impressing a pattern into one face of the sheet by embossingwith a die having lands and valleys to produce the desired pattern. Thepatterning step produces regions of increased density in the sheet.There is then applied over the entire surface of the sheet a liquidstain adapted to be absorbed to a different extent in the regions ofreduced density as opposed to the regions of higher density. A colordifferential is thus produced. If necessary, excess stain is removedfrom the surface of the sheet. The resulting patterned and stained sheetis then subjected to pressure to flatten the stained surface to thedesired extent.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesgenerally to the formation of such products as artificial wood veneerand patterned boards and planks having the desired pattern embedded inthe surface thereof in the form of varying concentrations of a suitablestain.

Description of the prior art Prior processes and methods for formingartificial veneers or patterned boards and the like have involvedembossing a wood surface followed by filling the embossed embossedregions with plastic compositions or similar filling materials. Thisprocess is exemplified by U.S. 1,947,-

459, Casto. Other processes have involved putting a resist or stencil ona thin wood surface and spraying or otherwise applying a coloringmaterial through the resist, as shown by U.S. 1,936,182, Beiger.

The present invention operates on a theory different from those of theseprior patents and enables one to produce an excellent artificial woodveneer, and other products, in an inexpensive manner. Natural woodveneer is growing scarcer as the supply of suitable trees diminishes,and accordingly, the present invention steps into the gap caused by thediminishing supply of the natural product.

SUMMARY OF THE INVENTION This invention relates to the method of makinga patterned wood sheet comprising forming a slurry of wood fibers inwater followed by the addition of any desirable materials such asbinders or Water repellants. A sheet is formed from the resultant slurryand a pattern is impressed in the surface of the resulting sheet bymeans of a suitable die platen or other convenient means for compressingsome portions of the fibrous surface of the sheet to a greater extentthan adjacent portions. This patterning results in relatively hard andsoft spots throughout the sheet to form the pattern. The sheet maybedried to any desirable extent. There is then applied to the patternedface of the sheet a liquid stain adapted to be absorbed into the face ofthe sheet, the absorption taking place to a different extent in the lessdense areas than in the increased dense areas resulting from thepatterning step. Since in the preferred method more of the liquid stainis absorbed in the regions 3,542,641 Patented Nov. 24, 1970 ice BRIEFDESCRIPTION OF THE DRAWING FIG. 1 is a simplified flow diagram of themethod of the present invention, and

FIG. 2 is a perspective view of the product of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The fibrous slurry from whichthe wood fiber sheet is to be made will be prepared in accordance withknown methods. Wood fibers which may come from steamcooked wood pulp,Puget Sound sulphite, kraft fibers, or wood fibers from any sourcesuitable for making a wetlaid sheet may be used as a starting material.The fibers are slurried in the water and any mechanical refining desiredmay then be carried out. The consistency of the slurry will generallyrange from about 0.2%-3%. If an artificial wood veneer is to be made, itis normally desirable to add 1%-10% by weight of a binder to the aqueousslurry of wood fibers in order to enhance the strength of the resultingthin sheet. The preferred binder will be a phenol-formaldehyde resin,normally in the B stage so as to be curable on the fibers upon theapplication of heat to the sheet. The resin may be deposited onto thefibers by any of the known processes, including the variety of beatersaturation processes available. Although elastomeric binders such as thesynthetic rubbers may be added to the aqueous slurry in the form oftheir latices in order to bind the fibers of the fibrous sheet, such isnot preferred in the present method due to the subsequent need for thepenetration of a liquid stain into the sheet itself. The liquid stainwill penetrate rubber-bonded sheets as will be explained below, butgreater sheet rigidity and clarity of pattern will be achieved by use ofthe phenolformaldehyde resin, or one of the other thermosetting resinsin the amounts stated.

It is preferred that water repellants be added to the slurry to bepicked up by the fibers prior to sheet formation. These water repellantsmay be any of the known water repellants normally used in thesheet-making processes. It is preferred to use tall oil acids, or any ofthe long-chain fatty acids possessing 12 carbon atoms or more in themolecule in order that the final product will repel moisture and willnot be subjected to undue moisture growth in use. The tall oil acids orother fatty acids or other water repellants are simply added to theaqueous slurry prior to sheet formation. They are added in an amount ofabout 2%-S% based on the weight of the wood fibers.

Sheet formation proceeds normally. If an artificial wood veneer is to beformed, the sheet will normally be thinner in the range of 0.015"0.030",while if a wallboard or plank is to be made, the sheet will normallyhave a thickness in the range of As- /2. Normal board and sheet-makingprocesses are used in the formation of the sheet. Water may be removedin the usual manner by allowing it to drain through a mold or through asheetmaking wire or cylinder.

As the next step, the formed sheet will normally have a patternimpressed in its surface while it is still wet, although some drying maytake place first. To achieve the requisite compression of the fibers itis preferred that at least about 30% by weight water remain in thesheet, although much larger amounts of water up to about 100% by weightmay remain in the sheet if the patterning step is applied with care. Thepreferred way to accomplish impressing a pattern into one face of thesheet is to simply press into that face a platen which has in it thereverse of the desired pattern. If an artificial wood veneer is to bemade, then the pattern to be impressed into the surface of the sheetwill simulate the grain of a suitable wood. A piece of natural wood maybe used as the embossing platen. For example, a piece of Douglas fir hasregions of hard and soft spots which may be emphasized by sandblastingthe surface of the natural wood with a relatively soft sandblastingmaterial such as ground walnut shells. The resulting die may be pressedinto the surface of the sheet made as described above to form in thesheet the grain pattern of the Douglas fir. A similar sequence of stepsmay be used to impress into the surface of the sheet the grained patternof walnut, oak, cherry, Philippine mahogany which is really a speciesknown as lauan, or any other desired wood pattern. It will beappreciated that metal plates having geometrical designs, human figures,or any desired pattern or design may also be prepared and used toimpress a pattern into the surface of the sheet.

The resulting sheet will have in it regions of varying density due tothe compression of the fibers by the elevated portions of the patternpressed into the surface of the sheet. A wide variety of densityvariations may be achieved across the surface of the sheet depending onthe pattern pressed into the surface of the sheet. A simple pattern oran exceedingly complex pattern may thus be achieved by establishingvarying degrees of compression of the fibers in one region as contrastedwith the fibers in another region of the face of the sheet.

After the pattern has been impressed in the sheet, and the sheetpreferably dried, a liquid stain is coated or sprayed across the entiresurface of the sheet. Normally it is preferred that the liquid stain beapplied to the surface of a sheet which contains less than about byweight water based on the weight of the fibers. This reduced Watercontent will ensure better pickup of the liquid stain by the sheet. Itis preferred that the water content of the sheet be in the range ofabout 2%7% by weight based on the weight of the fibers before the liquidstain is applied.

Since some areas of the patterned sheet are more dense than others, theliquid stain will be absorbed to a greater extent in the less denseareas than in the areas having a higher density. In this manner, colordifferentials will become apparent on the surface of the sheet accordingto the density of the fibers in any particular region. The liquid stainmay comprise any of the usual wood stains normally used to impartwalnut, mahogany, oak, cherry, or any other of the wood stain colorsnormally used. Since the sheet is made of wood fibers, these wood stainsmay be coated over the surface of the patterned sheet in any convenientmanner as by use of a doctor blade, roll coater, reverse roll coater,spray coating, curtain coating, and the like. Simple wiping on of theliquid stain may suffice. Depending on the density of the portions ofthe sheet which are to show a color different from the balance of thesheet, the liquid stain may be left on the surface of the sheet for afraction of a second or for several minutes or more. On a continuousproduction line it is convenient to apply the exact amount of stainneeded to produce the desired color differentials, and no excess willremain to be removed. The point is, if any excess of liquid stainexists, it should be removed. Another method of producing a colordifferential is to apply a bleaching solution that runs off theelevated, less dense regions and gathers and exerts a more pronouncedbleaching effect in the more dense regions.

Pigmented solutions or slurries, bleaching solutions,

dye solutions, and other similar coloring solutions may be used insteadof the normal liquid wood stains of commerce. It is necessary only thatthe liquid stain, whatever it is, penetrate the surface of the sheetmore in some areas than in others and impart to some regions a colordifferent from that of another region of the same face of the sheet.

After the removal of the excess liquid stain, if any, the sheet will bepressed to flatten to the desired extent the stained surface of thesheet. This pressing step serves to close the pores between the woodfibers, and the pressing step may serve to consolidate and strengthenthe entire sheet and, if heat is applied, to cure any thermosettingbinder used on the fibers in the original aqueous slurry. Since thevisual pattern effect is achieved by a coloring differential, thepattern surface of the stained sheet may be pressed completely flat andsmooth while still preserving and, in fact, enhancing the patternappearance. The pressing step will normally entail some degree ofheating in order to remove any residual moisture or solvents from thesheet. The pressing step may be followed by any lacqnering orclear-coating steps normally used on natural wood veneer to preserve andprotect the wood, and to bring out the grain or otherwise enhance thecolor differential. The lacquers or coatings may be glossy or flat asdesired, but they will all be sufiiciently transparent that thedifferential coloring effect may be seen through the coating.

If the present method is used to prepare an artificial wood veneer, theresulting product is a sheet which very closely resembles a natural woodveneer but which has far greater strength, flexibility and is much morecrackresistant than natural wood veneer. Additionally, due to thepresence of any desirable additives, the artificial wood veneer made bythe present method will have greater dimensional stability, will be moremoisture and fungus resistant, and may more efficiently be used in themanufacture of furniture and the like.

The following example illustrates an embodiment of the invention. Allparts are by weight unless otherwise stated.

EXAMPLE A sheet was made having the following formula: Ingredients PartsWood pulp, cooked 30 Wood flour 10 Phenol-formaldehyde resin, B stage 2Papermakers alum 1 Tall oil fatty acids l The pulp and wood flour wereslurried in 3,750 parts of water followed by one pass through a beater.The resin and tall oil fatty acids were then added followed by theaddition of the alum. The resulting slurry was poured into a mold and asheet having a thickness of 0.060" was prepared.

A sandblasted block of Douglas fir was placed on top of the wet sheet.The resulting embossed sheet was dried to a water content of 2%7% Thedried sheet was flooded with a walnut wood stain, and the excess stainwas wiped off. The regions of higher density-the depressed regionsdidnot absorb as much stain as the lower density regions; the lower densityregions were appreciably darker in appearance. The stained sheet was hotpressed at 200 F. for three minutes at a pressure of 500 pounds persquare inch. On spraying the cooled sheet with lacquer, a strongattractive flexible wood veneer sheet resulted.

We claim:

1. The method of making a smooth surfaced wood sheet having a simulatedwood grain pattern embedded in one surface thereof in the form ofvarying concentrations of wood stain comprising (a) forming in Water aslurry of wood fibers,

(b) forming a sheet from said slurry and removing up to 70% of the watertherefrom,

(c) impressing a three-dimensional wood grain pattern into one face ofsaid sheet by compressing the fibers in the pattern to a variabledensity greater than the density of the fibers in other regions of saidface,

(d) drying the sheet to a water content of from 2% to 7% by weight,based on the weight of the fibers,

(e) applying to said patterned face a uniform coating of a liquid woodstain whereby the stain is absorbed to a different extent in the lessdense regions than in the more dense regions of the sheet therebyproducing a variable color differential between said regions,

(f) removing any excess liquid stain from said patterned face, and then,

(g) pressing the patterned face to flatten the stained surface.

2. The method according to claim 1 in which said liquid stain is appliedto the surface of said sheet in an References Cited UNITED STATESPATENTS 1,867,575 7/1932 Loetscher 162-117 X 1,956,866 5/1934 Keller162-165 X 2,216,803 10/1940 Benda 117-11 X 2,402,966 7/1946 Linzell162-117 S. LEON BASHORE, Primary Examiner A. L. CORBIN, AssistantExaminer US. Cl. X.R.

